1. Field of the Invention
The present invention relates to the addressing of (any number of) participants of a bus system having a control unit, a bus starting from the control unit, and a plurality of participants that are sequentially connected to the bus.
2. Description of the Background Art
For minimizing wiring complexities, for example in vehicles, it is more and more common practice to transmit control signals for driving actuating elements via a bus to which, besides a control unit, the drive units for the actuator devices of the individual participants are connected. Combined to form a bus system are, for example, actuator devices of a vehicle air conditioner, a window lift, or front seats of a vehicle. To enable the control unit to selectively drive one or a plurality of actuators, addresses are assigned to the actuators. Conventionally, the addresses have been stored in the participants by programming or have been assigned to the participants via a plug or PIN coding. While programming is relatively unproblematic during manufacturing of a vehicle, it is more complicated when the overall participant, i.e. the actuator device plus the drive unit, is, for example, replaced in a repair shop. Further, with regard to the logistics, it is necessary that defined placement sequences are adhered to, which involves service inconvenience and a supply of pre-programmed (pre-addressed) components, which runs counter to the identical-part principle. Further, the plug coding may lead to a malfunction. Finally, it is also possible to realize the self-addressing of the participants of a bus system via switches for serially separating the bus connections between the participants. The drawbacks encountered in this regard are in particular the electrical disconnection of the bus line via active components and the large space requirement for bus systems that have numerous participants.
Automated address allocation methods for bus systems are known from EP 0 854 609 A1, DE 196 47 668 A1, DE 44 04 962 C2, DE 44 28 502 A1, WO 97/45983 A1 and DE 197 56 564 A1, for example.
From DE 40 38 992 C2 a method is known where the addresses of components of a danger-warning system are automatically assigned. Addressing is effected from the participant that is arranged the closest to the central unit to the participant that is arranged the furthest away from the central unit. Each participant includes a resistor in each of the two wires of a warning-system primary line, and a plurality of electrical and electronic components between the two wires. Further, each participant is provided with a short-circuit switch for short-circuiting the two wires. When a switch is short-circuited, the voltage drop across the two aforementioned resistors (with a measuring current being impressed onto the warning-system primary line) and can be measured. All participants are arranged in series in the warning-system primary line.
At the beginning of the addressing process a central control unit transmits a short-circuit signal for closing the short-circuit switches of all participants, which have not been addressed so far. Then a measuring current is impressed that is designed to cause a voltage drop in the first participant, as seen from the central unit, (i.e. a participant arranged closest to the central unit) of the group of participants not addressed so far. Thereafter, an address data signal is applied to the warning-system primary line. That participant, to which no address has been assigned and which previously detected a voltage drop, takes this address data signal into its address memory. Subsequently the short-circuit signal is allocated for the purpose of further addressing, wherein the short-circuit switch of the participant addressed before is not closed, but rather the short-circuit switches of all participants not addressed so far are activated. When the measuring current is being impressed, it generates a voltage drop, which is to be detected, in that participant of the group of participants not addressed so far that is now arranged closest to the control unit, such that this participant, in the next phase in which an address data signal is applied to the warning-system primary line, stores this address in its address memory and is thus also addressed. This process is continued until the last participant is addressed.
This known method proceeds from the ideal assumption that due to short-circuiting of the two wires of the warning-system primary line the overall measuring current flows via the short-circuit switch of that participant of the group of participants not addressed that is arranged closest to the central control unit. In the practice, electronic switches, which are used as short-circuit switches in the known method, have an on-resistance which is not negligible. Therefore a portion of the measuring current flows through the short-circuit switch of the adjacent participant not addressed so far and generates a voltage drop across this participant's resistors. It is thus necessary not only to take into account the fact that a voltage drop has been detected but also to detect the magnitude of this voltage drop. Further, it must be taken into consideration that, the farther away a participant not addressed so far is arranged from the central control unit, the more the measuring current and thus the detectable voltage drop are reduced. The reason for this is the fact that the measuring current must flow via the closed short-circuit switch of a participant located relatively far away from the central control unit via the resistors arranged in the wires of the warning-system primary line of the participant already addressed and disposed before the former participant. Evaluation and reliable detection of the voltage drops according to the known method are thus not trivial and involve high circuit complexities and programming effort.
In the German Patent Application DE 101 47 512 A1 a method is proposed which eliminates the problems described with regard to DE 40 38 992 C2. However in a specific embodiment the problem of relatively high BUS flows is encountered. These flows occur when the resistance of a pull-up 30 or a pull-down 40 of a central control unit 14 is lower than a joint resistance of all switches 26 of all participants 1 to 9. Although not shown in detail in FIGS. 1 to 13, DE 40 38 992 C2 describes this switch 26 as a switchable resistor. This fact forms the basis for the known principle.
In practice, the pull-up and/or the pull-down of the central control unit will display a current limitation which is due to current source behavior or resistance.
In the Figs. of DE 40 38 992 C2 the pull-up and/or the pull-down are illustrated as a resistor. Thus it is necessary that the individual current of each participant is dimensioned at a smaller value than the value of the current limitation of the central control unit divided by the number of participants. First, the measuring current available for generating a useful signal is thus so small that despite the high measuring effort only faulty measurements may be expected. Second, this maximum usable measuring current depends on the number of bus participants.